NREL Lamar Low Level Jet Project
Measurements needed for Wind Farms
In windy regions throughout the United States, modern wind turbine farms
are being built to generate electricity. A significant wind resource
resides in the western Great Plains of the United States. This region
frequently has the strongest winds at night in the form of a low level jet
(LLJ). A LLJ is a fast moving current of air that occurs one hundred to
several hundred meters above the surface of the
Earth. The LLJ can be several hundred meters thick with
slower winds above and below the jet.
To take advantage of higher
winds, turbine rotors are being installed at increasing heights. However,
recent measurements have also shown a higher likelihood of
encountering harmful turbulence at these heights.
Wind shear in the stratified flows below the LLJ
produces coherent (i.e., organized) turbulence which can damage or shut
down a wind turbine rotor. Few observations are available to define the severity and frequency of this
turbulence on the scale of the wind rotors.
The Lamar Low Level Jet Project
The National Renewable Energy Laboratory
Lamar Low Level Jet
Project (LLLJP) is a first step in determining the frequency and
severity of potentially damaging coherent turbulence at
turbine rotor heights.
The experiment location was a site where the nocturnal LLJ
routinely occurs during the warm season. The experiment results
will be used to design and deploy turbines.
The NREL/LLLJP site was at the Golden Prairie Wind Farm, under
construction by General Electic, south of
Lamar, CO. This will be the nation's third largest
wind farm with a maximum capacity of 162 megawatts, providing enough
electricity for the equivalent of about 160,000 households. For each of
the 108 turbines, the rotor height will be 80 m, and the length of each of
the three blades will be 40 m.
The experiment involved taking year-long high-frequency wind
tower-mounted anemometers at heights of 50, 65, 80,
and 120 m, and
a Doppler acoustic wind profiler (sodar).
The sodar was intended to take vertical wind profiles
above the tower measurements, however, the sodar signal routinely
disappeared at or below the LLJ height.
The program ended in September 2003 with a two-week intensive measurement campaign
using the NOAA
ETL High-Resolution Doppler Lidar
to map coherent
turbulence structures associated with the LLJ. The purpose of the lidar measurements
The ability of HRDL to effectively make these measurements was previously
demonstrated during the Cooperative Atmosphere-Surface Exchange Studies campaign
(CASES-99). The lidar
data from LLLJP is currently being analyzed.
- characterize the strength and height of the LLJ,
- compare the lidar-determined LLJ height with the top of the sodar signal,
- compare the lidar and tower velocity measurements, and
- characterize the intensity and extent of the coherent turbulence structures
in the LLJ.